Offshore platforms which the present invention is designed to protect are semirigid structures subject to damage by excessive shock loading. As drilling progresses to deeper waters in more open seas with the use of heavier supply boats and barges, it has become necessary to develop better protective systems. Such systems are generally attached to individual legs of the offshore platform. In the past, it has been the practice to use cast-off vehicle tires, usually large off-the-road or aircraft tires, mounted on a supporting column next to the platform leg, as shown for instance in Blackman U.S. Pat. No. 2,413,210 or Rolando U.S. Pat. No. 2,952,979, the latter showing the practice of filling the tires with cable or other material to prevent their excessive sagging or collapse. Some special structures have been built for this purpose, as shown for instance in Roach U.S. Pat. No. 3,005,435 and Schwall U.S. Pat. No. 2,424,635. However, each has attendant drawbacks. The cast-off vehicle tire systems involve the difficulty of finding a plurality of tires of the same large size, as well as the problems which arise when corded tires become waterlogged and sag. Moreover, deflated vehicle tires exhibit very poor shock absorption capabilities. Schwall, supra, resorted to making special rubber bumper moldings for this purpose, but such bumpers are mounted in a nonrotating manner and are therefore subject to early destruction. Roach shows rotating cushions, but the use of axles and bearings provides too fragile a structure to withstand open-sea battering.
An improved prior art protective structure has employed a bumper ring array supported on a vertical cylinder and supported at the lower end by a resilient shear mounting and at the upper end by a cylindrical shock cell. By reason of the differences in mounting at the top and bottom supports, unequal energy absorption has been experienced. That is, if a given force is applied distance X from the bottom, the reaction is different from the reaction produced by applying the same force the same distance from the top.